"""
Lookup Free Quantization
Proposed in https://arxiv.org/abs/2310.05737

In the simplest setup, each dimension is quantized into {-1, 1}.
An entropy penalty is used to encourage utilization.

Refer to
https://github.com/lucidrains/vector-quantize-pytorch/blob/master/vector_quantize_pytorch/lookup_free_quantization.py
https://github.com/theAdamColton/ijepa-enhanced/blob/7edef5f7288ae8f537f0db8a10044a2a487f70c9/ijepa_enhanced/lfq.py
"""

"""
Modified Open-MAGVIT2 code to use VQConfig.
"""

from math import log2, ceil
from collections import namedtuple

import torch
from torch import nn, einsum
import torch.nn.functional as F
from torch.nn import Module

from einops import rearrange, reduce, pack, unpack

from magvit2.config import VQConfig

# constants

LossBreakdown = namedtuple('LossBreakdown', ['per_sample_entropy', 'codebook_entropy', 'commitment', 'avg_probs'])

# helper functions

def exists(v):
    return v is not None

def default(*args):
    for arg in args:
        if exists(arg):
            return arg() if callable(arg) else arg
    return None

def pack_one(t, pattern):
    return pack([t], pattern)

def unpack_one(t, ps, pattern):
    return unpack(t, ps, pattern)[0]

# entropy

def entropy(prob):
    return (-prob * torch.log(prob + 1e-5)).sum(dim=-1)

# class

def mult_along_first_dims(x, y):
    """
    returns x * y elementwise along the leading dimensions of y
    """
    ndim_to_expand = x.ndim - y.ndim
    for _ in range(ndim_to_expand):
        y = y.unsqueeze(-1)
    return x * y

def masked_mean(x, m):
    """
    takes the mean of the elements of x that are not masked
    the mean is taken along the shared leading dims of m
    equivalent to: x[m].mean(tuple(range(m.ndim)))

    The benefit of using masked_mean rather than using
    tensor indexing is that masked_mean is much faster
    for torch-compile on batches.

    The drawback is larger floating point errors
    """
    x = mult_along_first_dims(x, m)
    x = x / m.sum()
    return x.sum(tuple(range(m.ndim)))

def entropy_loss(
    logits,
    mask=None,
    temperature=0.01,
    sample_minimization_weight=1.0,
    batch_maximization_weight=1.0,
    eps=1e-5,
):
    """
    Entropy loss of unnormalized logits

    logits: Affinities are over the last dimension

    https://github.com/google-research/magvit/blob/05e8cfd6559c47955793d70602d62a2f9b0bdef5/videogvt/train_lib/losses.py#L279
    LANGUAGE MODEL BEATS DIFFUSION — TOKENIZER IS KEY TO VISUAL GENERATION (2024)
    """
    probs = F.softmax(logits / temperature, -1)
    log_probs = F.log_softmax(logits / temperature + eps, -1)

    if mask is not None:
        avg_probs = masked_mean(probs, mask)
    else:
        avg_probs = reduce(probs, "... D -> D", "mean")

    avg_entropy = -torch.sum(avg_probs * torch.log(avg_probs + eps))

    sample_entropy = -torch.sum(probs * log_probs, -1)
    if mask is not None:
        sample_entropy = masked_mean(sample_entropy, mask).mean()
    else:
        sample_entropy = torch.mean(sample_entropy)

    loss = (sample_minimization_weight * sample_entropy) - (
        batch_maximization_weight * avg_entropy
    )

    return sample_entropy, avg_entropy, loss


class LFQ(Module):
    def __init__(self, config: VQConfig):
        super().__init__()

        # some assert validations

        assert exists(config.z_channels) or exists(config.codebook_size), \
            "either dim or codebook_size must be specified for LFQ"
        assert not exists(config.codebook_size) or log2(config.codebook_size).is_integer(), \
            f"your codebook size must be a power of 2 for lookup free quantization (suggested {2 ** ceil(log2(config.codebook_size))})"

        self.codebook_size = default(config.codebook_size, lambda: 2 ** dim)
        self.codebook_dim = int(log2(config.codebook_size))

        codebook_dims = self.codebook_dim * config.num_codebooks
        dim = default(config.z_channels, codebook_dims)

        has_projections = dim != codebook_dims
        self.has_projections = has_projections

        self.dim = dim
        self.codebook_dim = self.codebook_dim
        self.num_codebooks = config.num_codebooks

        # for entropy loss
        self.sample_minimization_weight = config.sample_minimization_weight
        self.batch_maximization_weight = config.batch_maximization_weight

        # for no auxiliary loss, during inference
        self.token_factorization = config.token_factorization  # only utilized in second stage
        if not self.token_factorization:  # for first stage model
            self.register_buffer('mask', 2 ** torch.arange(self.codebook_dim - 1, -1, -1), persistent=False)
        else:
            k = self.codebook_dim // 2
            self.register_buffer("mask", 2 ** torch.arange(k - 1, -1, -1), persistent=False)

        self.register_buffer('zero', torch.tensor(0.), persistent=False)

        # codes
        all_codes = torch.arange(config.codebook_size)
        bits = self.indices_to_bits(all_codes)
        codebook = bits * 2.0 - 1.0

        self.register_buffer('codebook', codebook, persistent=False)

    @property
    def dtype(self):
        return self.codebook.dtype

    def indices_to_bits(self, x):
        """
        x: long tensor of indices for constructing codebook, but actually not utilized in all the experiments.

        returns big endian bits
        """
        mask = 2 ** torch.arange(self.codebook_dim, device=x.device, dtype=torch.long)
        # x is now big endian bits, the last dimension being the bits
        x = (x.unsqueeze(-1) & mask) != 0
        return x

    def get_codebook_entry(self, x, bhwc):
        if self.token_factorization:
            k = self.codebook_dim // 2
            mask = 2 ** torch.arange(k - 1, -1, -1, device=x.device, dtype=torch.long)
        else:
            mask = 2 ** torch.arange(self.codebook_dim-1, -1, -1, device=x.device, dtype=torch.long)

        x = (x.unsqueeze(-1) & mask) != 0 # find its bit representation
        x = x * 2.0 - 1.0 #back to the float
        ## scale back to the desired shape
        b, h, w, c = bhwc
        x = rearrange(x, "b (h w) c -> b h w c", h=h, w=w, c=c)
        x = rearrange(x, "b h w c -> b c h w")
        return x

    def bits_to_indices(self, bits):
        """
        bits: bool tensor of big endian bits, where the last dimension is the bit dimension

        returns indices, which are long integers from 0 to self.codebook_size
        """
        assert bits.shape[-1] == self.codebook_dim
        indices = 2 ** torch.arange(
            0,
            self.codebook_dim,
            1,
            dtype=torch.long,
            device=bits.device,
        )
        return (bits * indices).sum(-1)

    def decode(self, x):
        """
        x: ... NH
            where NH is number of codebook heads
            A longtensor of codebook indices, containing values from
            0 to self.codebook_size
        """
        x = self.indices_to_bits(x)
        # to some sort of float
        x = x.to(self.dtype)
        # -1 or 1
        x = x * 2 - 1
        x = rearrange(x, "... NC Z-> ... (NC Z)")
        return x

    def forward(
        self,
        x,
        return_loss_breakdown=False,
        mask=None,
        return_loss=True,
        flip=False,
    ):
        """
        einstein notation
        b - batch
        n - sequence (or flattened spatial dimensions)
        d - feature dimension, which is also log2(codebook size)
        c - number of codebook dim
        """
        x = rearrange(x, 'b d ... -> b ... d')
        x, ps = pack_one(x, 'b * d')
        # split out number of codebooks

        x = rearrange(x, 'b n (c d) -> b n c d', c=self.num_codebooks)
        codebook_value = torch.Tensor([1.0]).to(device=x.device, dtype=x.dtype)
        quantized = torch.where(x > 0, codebook_value, -codebook_value)  # higher than 0 filled

        # calculate indices
        if self.token_factorization:
            k = self.codebook_dim // 2
            indices_pre = reduce((quantized[..., :k] > 0).int() * self.mask.int(), "b n c d -> b n c", "sum")
            indices_post = reduce((quantized[..., k:] > 0).int() * self.mask.int(), "b n c d -> b n c", "sum")
            # indices_post = 2**k + indices_post #shifter to the 1024
        else:
            if not flip:
                indices = reduce((quantized > 0).int() * self.mask.int(), 'b n c d -> b n c', 'sum')
            else:
                # not sure why this is necessary
                indices = reduce((quantized > 0).flip(-1).int() * self.mask.int(), 'b n c d -> b n c', 'sum')

        # entropy aux loss
        if self.training and return_loss:
            logits = 2 * einsum('... i d, j d -> ... i j', x, self.codebook)
            # the same as Euclidean distance up to a constant
            per_sample_entropy, codebook_entropy, entropy_aux_loss = entropy_loss(
                logits=logits,
                sample_minimization_weight=self.sample_minimization_weight,
                batch_maximization_weight=self.batch_maximization_weight
            )

            avg_probs = self.zero
        else:
            ## calculate the codebook_entropy needed for one batch evaluation
            #------------------------------------------------------------------
            # logits = 2 * einsum('... i d, j d -> ... i j', x, self.codebook)
            # probs = F.softmax(logits / 0.01, -1)
            # avg_probs = reduce(probs, "b n c d -> b d", "mean")
            # avg_probs = torch.sum(avg_probs, 0) #batch dimension
            #-------------------------------------------------------------------
            # if not training, just return dummy 0
            per_sample_entropy = codebook_entropy = self.zero
            entropy_aux_loss = self.zero
            avg_probs = self.zero

        # commit loss
        if self.training:
            commit_loss = F.mse_loss(x, quantized.detach(), reduction='none')

            if exists(mask):
                commit_loss = commit_loss[mask]

            commit_loss = commit_loss.mean()
        else:
            commit_loss = self.zero

        # use straight-through gradients (optionally with custom activation fn) if training
        quantized = x + (quantized - x).detach()  # transfer to quantized

        # merge back codebook dim
        quantized = rearrange(quantized, 'b n c d -> b n (c d)')

        # reconstitute image or video dimensions
        quantized = unpack_one(quantized, ps, 'b * d')
        quantized = rearrange(quantized, 'b ... d -> b d ...')

        if self.token_factorization:
            indices_pre = unpack_one(indices_pre, ps, "b * c")
            indices_post = unpack_one(indices_post, ps, "b * c")
            indices_pre = indices_pre.flatten()
            indices_post = indices_post.flatten()
            indices = (indices_pre, indices_post)
        else:
            indices = unpack_one(indices, ps, 'b * c')
            indices = indices.flatten()

        ret = (quantized, entropy_aux_loss, indices)

        if not return_loss_breakdown:
            return ret

        return ret, LossBreakdown(per_sample_entropy, codebook_entropy, commit_loss, avg_probs)